perhaps what we really need is a capabilities attribute on all `script` nodes, so the browser can determine if it needs to be loaded or not. For example:

perhaps what we really need is a capabilities attribute on all `script` nodes, so the browser can determine if it needs to be loaded or not. For example: <script src="usertiming-polyfill.js" provides="usertiming"></script> If the browser supports user timing, it does not load the script. If the browser does not support user timing (or does not support the `provides` attribute), it loads the script.